ATOMIC THEORY OF MAGNETISM || Magnetism and Matter Class 12, JEE & NEET

Magnetism and Matter Class 12 Notes will help you in your Exam Preparation and will also help in scoring good! The property of any object by virtue of which it can attract a piece of iron or steel is called magnetism. Here will study about the Atomic Theory of Magnetism.

Atomic Theory of Magnetism :

(1) Each atom behaves like a complete magnet having a north and south pole of equal strength. The electrons revolving around the nucleus in an atom are equivalent to small current loops which behaves as magnetic dipole.

(2) In unmagnetized magnetic substance these atomic magnets (represented by arrows) are randomly oriented and form closed chains. The atomic magnets cancel the effect of each other and thus resultant magnetism is zero.

1. In magnetised substance all the atomic magnets are aligned in same direction and thus resultant magnetism is non-zero.

The atomic theory explains the following facts in magnetism.

(1) Non existence of monopoles. The magnetic poles always exist in pairs and are of equal strength.

(2) When a magnet breaks than each part behaves like a complete magnet.

(3) Magnetisation of an electromagnet can be explained as alignment of atomic magnets in direction of magnetic field.

(4) This explains the phenomenon of saturation magnetization i.e. acquired magnetism remains constant even on increasing the external magnetizing field.

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Mind Map of Photo Electric Effect | Class 12, JEE & NEET – Download from here

Photoelectric Effect in Class 12 comprises variety of cases with important formulae and key points. So here is the mind map to help you in remembering all the formulas and important key concepts on finger tips.

Important Questions of PCMB Boards

Get important questions for Boards exams. Download or View the Important Question bank for all Subjects. These important questions will play significant role in clearing concepts. This question bank is designed by NCERT keeping in mind and the questions are updated with respect to upcoming Board exams. You will get here all the important questions for class 11 & Class 12.

# Class 11 PHYSICS

Rotational Motion

Gravitation

Simple Harmonic Motion

Circular Motion

Friction

Newton’s Laws Of Motion

Conservation Of Linear Of Momentum

Projectile Motion

Unit And Dimension

Heat And Thermodynamics

General Properties Of Matter

Motion In a Straight Line

# Class 12 PHYSICS

Electrostatics

Moving Charges & Magnetism

Wave Optics

Ray Optics

Semiconductor

Modern Physics

Alternating Current

Electromagnetic Induction

Capacitor

Current Electricity

# Class 11 CHEMISTRY

General Organic Chemistry

s-block

Chemical Bonding

Mole Concept

Boron Family

Carbon Family

Ionic Equilibrium

Electrochemistry

Periodic Properties

Thermodynamics and Thermochemistry

Chemical Equilibrium

Gaseous State

Atomic Structure

# Class 12 CHEMISTRY

Solution & Colligative Properties

Solid State

Chemical Kinetics

Carboxylic acids & Derivative

Aliphatic Hydrocarbon

Surface Chemistry

Co-ordination Compounds

Metallurgy

d & f block Elements

Noble Gases

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Solid State Short Notes for Class 12, IIT-JEE & NEET

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Solution & Colligative Properties | Question Bank for Class 12 Chemistry

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Solid State | Question Bank for Class 12 Chemistry

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Chemical Kinetics Solved Problems Class 12 Chemistry

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Aldehydes Ketones and Carboxylic Acids Class 12 Important Questions & Answers

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Aliphatic Hydrocarbon | Question Bank for Class 12 Chemistry

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Co-ordination Compounds | Question Bank for Class 12 Chemistry

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Noble Gases | Question Bank for Class 12 Chemistry

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Chemical Equilibrium | Question Bank for Class 11 Chemistry

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Class 11 Chemistry Thermodynamics Questions and Answers-Important for Exams

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The total entropy is the sum of the three contribution.

$\therefore \quad \Delta S_{\text {total}}=-26.0445-5.62-5.26$

$\Rightarrow \quad-36.9245 \mathrm{cal} K^{-1} \mathrm{mol}^{-1}$

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Applications of Colloids | Catalysis & its Types for Class 12, IIT-JEE, NEET

## Applications of Colloids

Colloids play an important role in our daily life and industry. Some of the important applications of colloids are listed below.

Indicators like fluoresce in function by adsorption of ions on to sol particles When silver nitrate solution is run into a solution of sodium chloride containing a fluoresce in a white precipitate of AgCl is first formed. At the end point the white precipitate turns sharply pink.

## Tanning

Animal leather (skin) is soft due to the presence of very fine globules oils and fats in the’ pores of skin. These globules are of colloidal in nature. When this soft leather (skin) is placed in salt water, these globules of oils and fats coagulate and settle down in water. Now when the animal hides tare dried, they become hand. This process of making soft leather to hard leather by dipping it in salt water is called tanning usually chromium salts are used for tanning.

## Clearing action of soaps and detergents

Dust and dirt particles on clothes are colloidal in nature soaps being sodium salts of higher fatty acids coagulates them which become suspension particles called micelle and roll out due to greater volume and greater mass.

## Industrial products

Paints, inks, synthetic plastics, rubber, graphite lubricants, cement, etc are all colloidal solutions.

Colloidal solution of graphite in water is called “Aqua dag” while that in Oil is called oil dag.

The phenomenon of increase in concentration at the surface due to molecular surface force is known as adsorption.

The solid substance on the surface of which adsorption takes place is called adsorbent. Examples of absorbents are activated charcoal, Pt, Pd, Ni etc.

## Sorption

lt may be defined as the process in which both adsorption and absorption take place simultaneously.

## Absorption

When a substance is uniformly distributed throughout the body of a solid of liquid, the phenomenon is called absorption.

Adsorption is due to the fact that the surface particles of the adsorbent are in different state than the particles inside the bulk. Inside the adsorbent all the forces acting between the particles are mutually balanced but on the surface particles are not surrounded by atoms or molecules of their kind on all sides and hence they possess unbalanced or residual attractive forces.

Depending upon the nature of forces between molecules of adsorbate and adsorbent, adsorption is of two types.

1. Nature of adsorbate: Readily liquefiable gases such as HCl, etc. are more. easily adsorbed by and adsorbent than the permanent gases etc.
2. Nature of absorbent: – Activated charcoal is a better adsorbent than transitional metals.

Pressure: – Extent of physical adsorption increases as the pressure of the gas increases, till a saturation point is reached.

Freundlich gave the following relationship between extent of adsorption

Where:

and are constants, depends upon the nature of adsorbate as well as adsorbent.

(a) At low pressure: is directly proportional to the pressure

(b) At high pressure: – The extent of adsorption,

becomes independent of pressure i.e. a. PO

(c) At intermediate pressure: – will depend upon the power of

pressure which lies between 0 and 1

or (i)

On taking logarithm on both sides of

(i) We get

(ii)

Expression (i) and (ii) are called Freundlich adsorption isotherm.

Expression (ii) represents a straight line. The slope of the line will be while its intercept on the log

axis will be

Temperature: Adsorption is accompanied by evolution of heat i.e. H is negative, so the rate of adsorption should decrease with rise in temperature. It is found to be so in case of physical adsorption. The effect of temperature is represented by an adsorption isobar.

Activation of adsorbent-An adsorbent can be activated either by heating or by bringing it in finely divided state, or by making its surface rough by rubbing. For example, charcoal is activated by heating it in vacuum at

## Catalysis

The phenomena in which the rate of a reaction is altered (increased or decrease) by the presence of a substance (Catalyst) is known as catalysis.

Catalytic reactions are divided into two types.

(a) Homogeneous catalysis

(b) Heterogeneous catalysis

## Homogeneous catalysis:

When the reactants and the catalyst are in the same physical state, i.e. in the same phase, it is called homogeneous catalysis. For example.

(i) Lead chamber process: – In this process for the manufacture of sulphuric acid NO (gas) is used as a catalyst.

(ii) Inversion of cane sugar- In aqueous solution is catalysed by dilute acid (Hydrogen ions)

(b) Heterogeneous catalysis: When the catalyst and the reactants are not in the same physical state i.e. not in the same phase, it is called heterogeneous catalysis. for example.

(i) Decomposition of

(ii) Haber process for

## TYPES OF CATALYSIS

(i) Positive catalysts: –The substance which increases the rate of a reaction is known as a positive catalyst. It decreases the energy of activation for the reaction. For example:

(ii) Negative catalysts: The substance which decreases the rate of chemical reaction is called negative catalyst or inhibitor. It increases the activation energy for the reaction. For example.

(iii) Auto catalysts: –When one of the products of the reaction begins to act as a catalyst, it is called auto-catalyst for example. In the initial stages the reaction is slow but as soon as the products come into existence the the reaction rate increases

(iv) Induced catalyst:- When a chemical reaction enhances the rate of another chemical reaction it is called induced catalysis. For example:-

Soduim arsenite solution is not oxidised by air. If however, air is passed through a mixture of both of them undergo simultaneous oxidation. The oxidation of sodium sulphite, thus influences the oxidation of sodium arsenite.

Promoters: Those substance which do not themselves act as catalysts but their presence increases the activity of a catalyst are called catalytic promoters or catalyst for a catalyst. Example: In the Haber process for the synthesis of ammonia, Fe is the catalyst while molybdenum (Mo) acts as promoter.

Catalytic Poison: –The substance whose presence decreases or destroy the activity of a catalyst is called catalytic poison. For example:- Carbon monoxide or in hydrogen gas, acts as a poison for Fe catalyst in the Haber process for acts as poison for asbestos in contact process for

Inhibitors: – Those substances which retard rate of a chemical reaction are known as inhibitor. For example: glycerol or acetamide decrease the rate of decomposition of hydrogen peroxide.

General characteristics of catalysts:

(i) A catalyst remains unchanged in mass and chemical composition but change their physical state.

(ii) Only a very small amount of catalyst is sufficient to catalyse a reaction.

(iii) A catalyst does not initiate a reaction & does not controlled on chemical Rxn.

(iv) When a catalyst is a solid, it is usually more efficient where used in finely divided form.

(v) Generally, catalyst does not change the nature of products.

(vi) A catalyst does not change the equilibrium state of a reversible reaction but help to time achieve of equilibrium state. or position of equilibrium.

(vii) The catalysts are generally specific in nature.

(viii) Change rate constant of Rxn.

(ix) does not change free energy of Rxn.

THEORIES OF CATALYSIS

Intermediate compound formation theory: -This theory is explaining homogeneous catalysis mainly. According to this theory, the catalyst combines with one of the reactants to give an intermediate compound. This compound intermediately reacts with the other reactants and gives the product and regenerates the catalyst in its original form.

Thus, the reactants do not directly combine with each other, instead they react through the catalyst which provides an alternative pathway which involves lesser energy of activation.

For example: -The function of nitric oxide (NO) as a catalyst in the formation of is explained as follows.

Adsorption theory: – This theory is explaining the heterogeneous catalysis. The role of a solid catalyst in enhancing the reaction rate is explained on the basis of this theory in the following steps.

(i) The reactant molecules are absorbed on the surface of the catalyst at adjacent points. Adsorption leads to higher concentration of the adsorbed reactant on the surface of a catalyst.

(ii) As adsorption is an exothermic process, the heat of adsorption provides the necessary activation energy for the chemical reaction to proceed.

(iii) The adsorbed reactant molecules are tied on the solid sold surface of the catalyst. The bonds between the atoms of chemisorption  reactant molecules are weakened. The reactant molecules of sufficient energy combine together and with the surface of the catalyst to form surface activated complex.

This adsorbed activated complex is decomposed to form ‘products as a definite faster rate.

Catalysts in Industry: – Some of the important processes and their catalyst are given in below.

### Click Here to Practice JEE Main Previous Year questions of Surface Chemistry

Coagulation of Colloids | Methods | Associated Colloids for Class 12, IIT-JEE, NEET

Learn about Coagulation of Colloids, Electrophoresis, water in oil emulsion, oil in water emulsion, Associated Colloids and more. Get to know about the Colloid Protection here.

Charge on Colloidal Particles

Helmholtz Electrical Double Layer

Electrophoresis

Electro-osmosis

Coagulation of Colloids & its methods

Hardy Schulze Law

Protective Colloids

Emulsions

Associated Colloids

Gels

## Charge on colloidal particles

Colloidal particles always carry an electric charge. The mutual forces of repulsion between similarly charged particles prevent them from aggregating and settling under the action of gravity. This gives stability to the sole A list of common sols with the type of change on their particles is given ahead.

## Helmholtz Electrical Double Layer

The surface of a colloidal particle acquires a type by selective adsorption of a layer of positive ions around it. This layer attracts counter ions from the medium which form a second layer of -ve charges. The combination of the two layers of +ve and-ve charges around the sol particle was called Helmholtz double layer. According to modern view, the first layer of ions is firmly held and is termed fixed layer while the second layer is mobile which is termed as diffused layer.

The combination of the compact and diffused layer is referred as the stern double layer. The diffused layer is only loosely attached to the particles surface and moves in the opposite direction under an applied electric field. The potential difference between., the fixed layer and the diffused layer of opposite charge is called electro kinetic potential or zeta potential.

### Electrophoresis Meaning

If electric potential is applied across two platinum electrodes dipping in a colloidal solution, the colloidal particles move towards one or the other electrode, due to charge them, The movement of sol particles under an applied electric potential is called “Electrophoresis”, Depending upon the direction of movement of particles towards cathode, or anode electrophoresis can be called “cataphoresis’ or ‘Anaphoresis”.Electrophoresis provides and experimental proof to show that the colloidal particles are charged particles.

### Electro-osmosis

The medium will move in opposite direction to the dispersed phase under the influence of applied electric potential. The movement of dispersion medium under the influence of applied potential is known as ‘Electro – osmosis’.

## Coagulation of Colloids

We know that the stability of a lyophobic sol is due to the adsorption of positive or negative ions by the dispersed particles. The repulsion forces between the charged particles do not allow

them to settle. If somehow, the charge is removed there is nothing to keep the particles apart from each other. In such cases they aggregate or flocculate and settle down under the action of gravity the flocculation and settling down of the discharged sol particles is called coagulation or the precipitation can be brought about in four ways

### Methods of Coagulation

(b) By electrophoresis.

(c) By mixing two oppositely charged sols.

(d) By boiling.

### (a) By addition of electrolytes

When an electrolyte is added in excess to a sol, then the electrolyte furnishes both the type of ions in solution. The oppositely charged ions get adsorbed on the surface of colloidal particles this causes neutralization and there by the size and mass of colloidal particle increases and it becomes a suspension particle. Due to greater volume and greater mass these suspension particles settle down i.e. they coagulate. The ion responsible for neutralization of charge on the particle is called the flocculating ion,

### Hardy Schulze Law

states that the precipitating effect of an ion on dispersed phase of opposite charge increases with the valence of the ion.

The higher the valency of the flocculating ion, the greater is its precipitating power. Thus, for the precipitation of

solutions.

Similarly for precipitating sol (positive) the precipitating power of and is in the order

### FLOCCULATION VALUE

The minimum ,concentration of an electrolyte in milli moles per litre required to cause precipitation of a sol in 2 hours is called FLOCCULATION VALUE. The smaller the flocculating value, the higher will be the coagulating power of the ion.

### (b) By Electrophoresis

During electrophoresis the charged sol particles migrate towards the electrode of opposite sign. There they deposit their charge and then get coagulated (As the neutral particles can aggregate and change to suspension particles.

### (c) By mixing two oppositely charged sols-

The neutral coagulation of two sols of opposite charge can be affected by mixing them. For e.g. (positive) sol and Arsenious sulphide (negative sol) when mixed join and coagulate.

### (d) By boiling

Sols such as sulphur and silver halides disperse in water disperse in water, get coagulated when boiled due to increased collisions between sol particles and water molecules, which removes the adsorbed charged layer from the sol and therefore the sol particles settle down.

## Protective Colloids : Protection or Protective action.

Lyophobic sols are readily precipitated by small amounts of electrolytes. However, these sols often stabilized by the addition of Lyophilic sols.

The property of Lyophilic soles to prevent the precipitation or coagulation of a lyophobic salt is called protection. The Lyophilic sol used to protect a lyophobic sol from precipitation is referred to as a protective colloid. Lyophilic sols form a thin layer around lyophobic sol or around the ions furnished by electrolyte and therefore the coagulation cannot take place (as the size does not increase much). Gelatine, Albumen, Gum Arabia, Potato Starch are some of the examples of protective colloids.

The Lyophilic colloids differ in their protective power. The protective power is measured in terms of “Gold number introduced by Zsigmondy.

The number of milligrams of a hydrophilic colloid that will just prevent the precipitation of 10 of gold solon addition of 1 of 10 solution is known as gold number of that protector (Lyophilic colloid) On the onset of precipitation of the gold sol is indicated by a colour change from red to blue when the particle size just increases.

The smaller the gold number of a protective Lyophilic colloid, greater is its protection power.

Gold Number of some Lyophilic colloids

Protection Capacity

Gelatine and starch have the maximum and minimum protective powers.

## Emulsions

These are liquid-liquid colloidal systems. There are two types Emulsions

(i) Oil dispersed in water (o/w types)

(ii) Water Dispersed in oil (w/o types)

water in oil emulsion Examples
Oil in water Emulsion

In the first type water acts dispersion medium examples of this type of emulsions are milk and vanishing cream. In milk, liquid fat is dispersed in water. In the second system oil acts as dispersion medium common examples of this type are butter and cream.

Emulsions of oil and water are unstable and sometimes they separate into two layers on standing. For stabilization an of an emulsion, a third component called emulsifying agent is usually added. The emulsifying agent form an inter facial film between suspended particles and the medium. The Principal agent for of emulsions are proteins, gums, soaps, etc. for w/o emulsion the principal emulsifying agents are heavy metal salts of fatty acids, long chain alcohols etc.

## Associated Colloids [Micelles]

Substances whose molecules aggregates to form particles of colloidal dimensions are called associated colloids.

The molecules of soaps and detergents are usually smaller than the colloidal particles. However, in concentrated solutions, these molecules associated and form aggregates of colloidal size. These aggregates of soaps or detergent molecules are called micelles. Soaps and detergents are strong electrolytes and gives ions when dissolved in water

The negative ions aggregate to form a micelle of colloidal size. The negative ion has a long Hydrocarbon chain and a polar groupin water it directed towards the center while the soluble polar head is on the surface in contact with water. The charge on the micelle is responsible for the stability of this system.

## Gels

A gel is a jelly like colloidal system in which a liquid is dispersed in a solid medium.

Gels may be classified into two types

(a) Elastic gels- These are those which possesses the property of elasticity. They change their shape on applying force and return to original shape when the force is removed. Gelatine, starch and soaps are examples substances which form elastic gels.

(b) Non- elastic gels- These are the gels which are rigid ego Silica gel. These are prepared by appropriate chemical action. Thus, silica gel is produced by adding concentrated Hydrochloric Acid to sodium silicate solution of the correct concentration.

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